The present invention relates to an air-conditioning system comprising a plurality of indoor units and outdoor units connected thereto, or in particular to a large air-conditioning system used and suitably maintained in large buildings.
A conventional air-conditioning system of comparatively large scale is disclosed in JP-A-9-79654, for example, in which a plurality of air conditioners are known to be connected to a network through a gateway to meet the requirement of maintenance/control and system development.
An air-conditioning system is also described in JP-A-5-272795, wherein in order to reduce the cost of wiring various signal lines, the AC voltage of a power line for supplying power to the outdoor units and the indoor units is superposed with a power-line superposed signal such as a high-frequency signal of 10 to 450 kHz thereby to combine the signal line and the power line into a single common line.
In the prior art described above, a sufficient consideration fails to be given to the facts that the transmission line may be erroneously wired between the air conditioners, the operation data for the air conditioners are collected during the inspection work, the wiring distance is limited by the data deterioration due to the wiring length and the environment, and the voltage or the number of phases may be different between each outdoor unit and the corresponding indoor unit.